High-power octave-bandwidth helix traveling-wave tubes employing velocity resynchronization and dispersion shaping techniques

High-power helix tubes employing velocity resynchronization techniques have been developed that demonstrate efficiencies of 40-50 percent over an octave bandwidth with peak efficiencies in the excess of 60 percent. Shield-loading techniques were used to reduce the phase velocity dispersion generally experienced at low values of the propagation parameter γaand to extend the operating bandwidth to the low γaregion. The interaction impedance is high in this region and the velocity resynchronization schemes are particularly effective because of favorable beam-circuit wave interaction.